CBSE Class 12-science Answered

The formation of image by a convex lens 'L' is show in fig. AB is object and A'B' is the image.

Let distance of object AB from lens = u

Distance of image A'B' from lens = v

Focal length of lens = f.

Triangles ABC and A'B'C are similar

Similarly triangles PCF and A'B' are similar

But PC = AB

              ..........(2)

From (1) and (2), we get

                    ..........(3)

From sign convection, CB =-u, CB' = v CF = f and FB' =CB' - CF = v - f

Subsituting this value in (3), we get, -

or                   -u (v - f) = vf or - uv + uf = vf

Dividing througout by uvf, we get 

                                   .........(4)

OR

The formation of image by a concave lens 'L' is shown in fig. AB is object and A'B' is the image.

Answered by | 08 Jul, 2014, 03:39: PM